Take them somewhere beautiful, at a beautiful time, that they're unlikely to know much about.

I proposed to my girl (now wife) while on a ferry crossing Sydney Harbour at night. The lights at night glittered on the water, and she was blown away by it. Only cost a ferry ticket too. We bought rings later.

What I personally did was build a "Hallway of memories" for my proposal. Each room has a dedicated purpose and color pallat. I made the rooms out of streamers, and hung up pictures in each streamer room. It's a bit time consuming, but not all too expensive.

For example, my first room was Geek Squad, because that's where we met. The colors were Orange, black, and write. The next room was the hospital, because that's where I realized she was fully dedicated to me. Those colors were black, white and red. I had her walk through a streamer tardis first, as it was taking her back through time.

What I personally did was build a "Hallway of memories" for my proposal. Each room has a dedicated purpose and color pallat. I made the rooms out of streamers, and hung up pictures in each streamer room. It's a bit time consuming, but not all too expensive.

For example, my first room was Geek Squad, because that's where we met. The colors were Orange, black, and write. The next room was the hospital, because that's where I realized she was fully dedicated to me. Those colors were black, white and red. I had her walk through a streamer tardis first, as it was taking her back through time.

This is a stretch, but... you could propose via webcomic... make a link that pops up...

Gosh sounds like something my boyfriend would do!! Lol.....
HE made a comic about our lives if we were in a zombie apocolypse. LOL
And now all I can imagine is reading a page in this comic, us sitting in some
abandoned restaurant him about to pop the question and BAM zombies
start beating on the windows and and we get up to start fighting zombies off of us he yells across the room
"IF WE EVER GET OUT OF THIS, WILL YOU MARRY ME?!?!"
And for some random reason Train starts playing in the background........
"Maaaaaaarrrrrrrrrrry MEEEEEEEEE, If I ever get the nerve to say 'HELLO' in this cafe......."

Yes off course..you can do that with the help of a web comic I am being very biased but as a web comic lover, I think the gift of clear expression and genuine emotions with fun quotient is best ensure this way